As is made evident in the above-referenced U.S. Patent, in the treatment of cancer and macular degeneration with photodynamic therapy (PDT), a class of photosensitizing compounds has been developed by a number of drug companies that are either selectively retained in, or are preferentially produced by, rapidly dividing cells. These dye-like molecules, when exposed to laser light in the visible or UV region, are excited to the triplet state where they have the capacity to promote molecular oxygen to its first excited singlet (.sup.1 O.sub.2). This species of molecular oxygen is believed to be cytotoxic and to cause local necrosis of tumor cells.
One particular drawback of the technique, however, is the limit in penetration depth inherent in using visible light as an activation mechanism. Additionally, the use of lasers or lamps as an activation source may require the use of expensive or complicated delivery systems. Furthermore, diagnosis and treatment of internal cancer sites may be invasive, and require the use of fiber optic catheters, endoscopes, or similar instruments.
Similar problems can arise when performing a diagnostic procedure to determine a presence of and/or location of abnormal cell tissue.